<time.h>: Add timegm(), timelocal() and others.

Add timegm(), timelocal(), time2posix() and posix2time() to the
C library.

Change-Id: I34d5771ed83dd994870a5ca58a511d01898b1ffb
diff --git a/libc/docs/CHANGES.TXT b/libc/docs/CHANGES.TXT
index bc641f4..67b9e76 100644
--- a/libc/docs/CHANGES.TXT
+++ b/libc/docs/CHANGES.TXT
@@ -9,6 +9,8 @@
 
 - <sys/cdefs.h>: Include <android/api-level.h>
 
+- <time.h>: Add timegm(), timelocal(), time2posix() and posix2time()
+
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 Differences between Android 2.3 and Android 2.2: